Prime Checker & Factorization
Instantly check whether a number is prime and see its prime factorization — runs 100% in your browser with no upload.
60 = 2^2 × 3 × 5
🔒 Checked in your browser — nothing is uploaded.
What this tool does
Type any whole number and this tool tells you whether it is prime, or breaks it down into its prime factorization such as 60 = 2^2 × 3 × 5. It uses trial division up to the square root of the number, so even large values up to about a trillion (10^12) resolve almost instantly. A number is prime when it is 2 or greater and has no divisors other than 1 and itself; 0, 1, negatives and decimals are not prime and have no factorization.
Why factorization matters
Prime factorization is the backbone of number theory and shows up everywhere from simplifying fractions and finding least common multiples to understanding how encryption keys are built. Because every integer greater than 1 has a unique prime factorization, the breakdown you see here is the one and only correct answer for that number. Everything is computed locally in your browser, so you can check as many numbers as you like without limits.
Frequently asked questions
How large a number can I check?
You can reliably check whole numbers up to about 10^12 (a trillion). Trial division runs only up to the square root of the number, so results appear almost instantly even for large inputs.
Why are 0, 1 and negative numbers not prime?
By definition a prime is a whole number of 2 or greater with exactly two divisors, 1 and itself. 0 and 1 do not meet that rule, and prime factorization is defined only for integers greater than 1, so the tool asks for a whole number of 2 or greater.
Is my number sent to a server?
No. Everything runs entirely in your browser using JavaScript. Nothing you type is uploaded, logged or stored anywhere.